# C++ Standard Library headers

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< cpp

The interface of C++ standard library is defined by the following collection of headers.

### Multi-purpose headers
<cstdlib> | General purpose utilities: program control, dynamic memory allocation, random numbers, sort and search
<execution> (C++17) | Predefined execution policies for parallel versions of the algorithms and execution control components(since C++26)
### Language support library
<cfloat> | Limits of floating-point types
<climits> | Limits of integral types
<compare> (C++20) | Three-way comparison operator support
<coroutine> (C++20) | Coroutine support library
<csetjmp> | Macro (and function) that saves (and jumps) to an execution context
<csignal> | Functions and macro constants for signal management
<cstdarg> | Handling of variable length argument lists
<cstddef> | Standard macros and typedefs
<cstdint> (C++11) | Fixed-width integer types and limits of other types
<exception> | Exception handling utilities
<initializer_list> (C++11) | std::initializer_list class template
<limits> | Query properties of arithmetic types
<new> | Low-level memory management utilities
<source_location> (C++20) | Supplies means to obtain source code location
<stdfloat> (C++23) | Fixed-width floating-point types
<typeindex> (C++11) | std::type_index
<typeinfo> | Runtime type information utilities
<version> (C++20) | Supplies macros for verifying implementation status of library
### Concepts library
<concepts> (C++20) | Fundamental library concepts
### Diagnostics library
<cassert> | Conditionally compiled macro that compares its argument to zero
<cerrno> | Macro containing the last error number
<debugging> (C++26) | Debugging library
<stacktrace> (C++23) | Stacktrace library
<stdexcept> | Standard exception types
<system_error> (C++11) | Defines std::error_code, a platform-dependent error code
### Memory management library
<memory> | High-level memory management utilities
<memory_resource> (C++17) | Polymorphic allocators and memory resources
<scoped_allocator> (C++11) | Nested allocator class
### Metaprogramming library
<ratio> (C++11) | Compile-time rational arithmetic
<type_traits> (C++11) | Compile-time type information utilities
### General utilities library
<any> (C++17) | std::any class
<bit> (C++20) | Bit manipulation functions
<bitset> | std::bitset class template
<expected> (C++23) | std::expected class template
<functional> | Function objects, Function invocations, Bind operations and Reference wrappers
<optional> (C++17) | std::optional class template
<tuple> (C++11) | std::tuple class template
<utility> | Various utility components
<variant> (C++17) | std::variant class template
### Containers library
<array> (C++11) | std::array container
<deque> | std::deque container
<flat_map> (C++23) | std::flat_map and std::flat_multimap container adaptors
<flat_set> (C++23) | std::flat_set and std::flat_multiset container adaptors
<forward_list> (C++11) | std::forward_list container
<inplace_vector> (C++26) | std::inplace_vector container
<list> | std::list container
<map> | std::map and std::multimap associative containers
<mdspan> (C++23) | std::mdspan view
<queue> | std::queue and std::priority_queue container adaptors
<set> | std::set and std::multiset associative containers
<span> (C++20) | std::span view
<stack> | std::stack container adaptor
<unordered_map> (C++11) | std::unordered_map and std::unordered_multimap unordered associative containers
<unordered_set> (C++11) | std::unordered_set and std::unordered_multiset unordered associative containers
<vector> | std::vector container
### Iterators library
<iterator> | Range iterators
### Ranges library
<generator> (C++23) | std::generator class template
<ranges> (C++20) | Range access, primitives, requirements, utilities and adaptors
### Algorithms library
<algorithm> | Algorithms that operate on ranges
<numeric> | Numeric operations on values in ranges
### Strings library
<cstring> | Various narrow character string handling functions
<string> | std::basic_string class template
<string_view> (C++17) | std::basic_string_view class template
### Text processing library
<cctype> | Functions to determine the category of narrow characters
<charconv> (C++17) | std::to_chars and std::from_chars
<clocale> | C localization utilities
<codecvt> (C++11)(deprecated in C++17)(removed in C++26) | Unicode conversion facilities
<cuchar> (C++11) | C-style Unicode character conversion functions
<cwchar> | Various wide and multibyte string handling functions
<cwctype> | Functions to determine the category of wide characters
<format> (C++20) | Formatting library including std::format
<locale> | Localization utilities
<regex> (C++11) | Classes, algorithms and iterators to support regular expression processing
<text_encoding> (C++26) | Text encoding identifications
### Numerics library
<cfenv> (C++11) | Floating-point environment access functions
<cmath> | Common mathematics functions
<complex> | Complex number type
<linalg> (C++26) | Basic linear algebra algorithms (BLAS)
<numbers> (C++20) | Math constants
<random> (C++11) | Random number generators and distributions
<simd> (C++26) | Data-parallel types and operations on these types
<valarray> | Class for representing and manipulating arrays of values
### Time library
<chrono> (C++11) | C++ time utilities
<ctime> | C-style time/date utilities
### Input/output library
<cinttypes> (C++11) | Formatting macros, `intmax_t` and `uintmax_t` math and conversions
<cstdio> | C-style input-output functions
<filesystem> (C++17) | std::filesystem::path class and supporting functions
<fstream> | std::basic_fstream, std::basic_ifstream, std::basic_ofstream class templates and typedefs
<iomanip> | Helper functions to control the format of input and output
<ios> | std::ios_base class, std::basic_ios class template and typedefs
<iosfwd> | Forward declarations of all classes in the input/output library
<iostream> | Several standard stream objects
<istream> | std::basic_istream class template and typedefs
<ostream> | std::basic_ostream, std::basic_iostream class templates and typedefs
<print> (C++23) | Formatted output library including std::print
<spanstream> (C++23) | std::basic_spanstream, std::basic_ispanstream, std::basic_ospanstream class templates and typedefs
<sstream> | std::basic_stringstream, std::basic_istringstream, std::basic_ostringstream class templates and typedefs
<streambuf> | std::basic_streambuf class template
<strstream> (deprecated in C++98)(removed in C++26) | std::strstream, std::istrstream, std::ostrstream
<syncstream> (C++20) | std::basic_osyncstream, std::basic_syncbuf and typedefs
### Concurrency support library
<atomic> (C++11) | Atomic operations library
<barrier> (C++20) | Barriers
<condition_variable> (C++11) | Thread waiting conditions
<future> (C++11) | Primitives for asynchronous computations
<hazard_pointer> (C++26) | Hazard pointers
<latch> (C++20) | Latches
<mutex> (C++11) | Mutual exclusion primitives
<rcu> (C++26) | Read-copy update mechanisms
<semaphore> (C++20) | Semaphores
<shared_mutex> (C++14) | Shared mutual exclusion primitives
<stop_token> (C++20) | Stop tokens for std::jthread
<thread> (C++11) | std::thread class and supporting functions

### C compatibility headers

For some of the C standard library headers of the form `xxx.h`, the C++ standard library both includes an identically-named header and another header of the form `cxxx` (all meaningful `cxxx` headers are listed above). The intended use of headers of form `xxx.h` is for interoperability only. It is possible that C++ source files need to include one of these headers in order to be valid ISO C. Source files that are not intended to also be valid ISO C should not use any of the C headers.

With the exception of `complex.h`, each `xxx.h` header included in the C++ standard library places in the global namespace each name that the corresponding `cxxx` header would have placed in the std namespace.

These headers are allowed to also declare the same names in the std namespace, and the corresponding `cxxx` headers are allowed to also declare the same names in the global namespace: including `<cstdlib>` definitely provides std::malloc and may also provide ::malloc. Including `<stdlib.h>` definitely provides ::malloc and may also provide std::malloc. This applies even to functions and function overloads that are not part of C standard library.

Notes: `xxx.h` headers are deprecated in C++98 and undeprecated in C++23. These headers are discouraged for pure C++ code, but not subject to future removal.

<assert.h> | Behaves same as `<cassert>`
<ctype.h> | Behaves as if each name from `<cctype>` is placed in global namespace
<errno.h> | Behaves same as `<cerrno>`
<fenv.h> (C++11) | Behaves as if each name from `<cfenv>` is placed in global namespace
<float.h> | Behaves same as `<cfloat>`
<inttypes.h> (C++11) | Behaves as if each name from `<cinttypes>` is placed in global namespace
<limits.h> | Behaves same as `<climits>`
<locale.h> | Behaves as if each name from `<clocale>` is placed in global namespace
<math.h> | Behaves as if each name from `<cmath>` is placed in global namespace, except for names of mathematical special functions
<setjmp.h> | Behaves as if each name from `<csetjmp>` is placed in global namespace
<signal.h> | Behaves as if each name from `<csignal>` is placed in global namespace
<stdarg.h> | Behaves as if each name from `<cstdarg>` is placed in global namespace
<stddef.h> | Behaves as if each name from `<cstddef>` is placed in global namespace, except for names of `std::byte` and related functions
<stdint.h> (C++11) | Behaves as if each name from `<cstdint>` is placed in global namespace
<stdio.h> | Behaves as if each name from `<cstdio>` is placed in global namespace
<stdlib.h> | Behaves as if each name from `<cstdlib>` is placed in global namespace
<string.h> | Behaves as if each name from `<cstring>` is placed in global namespace
<time.h> | Behaves as if each name from `<ctime>` is placed in global namespace
<uchar.h> (C++11) | Behaves as if each name from `<cuchar>` is placed in global namespace
<wchar.h> | Behaves as if each name from `<cwchar>` is placed in global namespace
<wctype.h> | Behaves as if each name from `<cwctype>` is placed in global namespace

#### Special C compatibility headers

The header `<stdatomic.h>` declares names which are also provided in the C standard library, and defines the `_Atomic` macro which is a keyword in C. Unlike other `xxx.h` headers, corresponding `<cstdatomic>` is not provided.

<stdatomic.h> (C++23) | Defines `_Atomic` and provides corresponding components in the C standard library

#### Empty C headers

The headers `<complex.h>`, `<ccomplex>`, `<tgmath.h>`, and `<ctgmath>` do not contain any content from the C standard library and instead merely include other headers from the C++ standard library.

<ccomplex> (C++11)(deprecated in C++17)(removed in C++20) | Simply includes the header `<complex>`
<complex.h> (C++11) | Simply includes the header `<complex>`
<ctgmath> (C++11)(deprecated in C++17)(removed in C++20) | Simply includes the headers `<complex>` and `<cmath>`: the overloads equivalent to the contents of the C header `tgmath.h` are already provided by those headers
<tgmath.h> (C++11) | Simply includes the headers `<complex>` and `<cmath>`

#### Meaningless C headers

The headers `<ciso646>`, `<cstdalign>`, and `<cstdbool>` are meaningless in C++ because the macros they provide in C are language keywords in C++.

<ciso646> (removed in C++20) | Empty header. The macros that appear in `iso646.h` in C are keywords in C++
<cstdalign> (C++11)(deprecated in C++17)(removed in C++20) | Defines one compatibility macro constant
<cstdbool> (C++11)(deprecated in C++17)(removed in C++20) | Defines one compatibility macro constant
<iso646.h> | Has no effect
<stdalign.h> (C++11) | Defines one compatibility macro constant
<stdbool.h> (C++11) | Defines one compatibility macro constant

#### Unsupported C headers

The C headers `<stdatomic.h>`,(until C++23) `<stdnoreturn.h>`, and `<threads.h>` are not included in C++ and have no `cxxx` equivalents.

### Experimental libraries

C++ TR's/TS's also define several collections of headers.

### See also

C documentation for C Standard Library headers

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